As a valve opening/closing timing control apparatus, JP 2011-241823 A (Reference 1) discloses a technology in which a driven side rotator (a stator in Reference 1), which is connected to a camshaft, and a driving side rotator (a driving wheel), which rotates in cooperation with a crankshaft, are provided, and a hydraulic valve is accommodated in a connecting bolt (a bush), which connects and fixes the driven side rotator to the camshaft.
In the technology of Reference 1, a sleeve is provided inside the connecting bolt, a spool (a hollow-shaped piston) is slidably fitted onto the sleeve, and an actuator is provided outside the connecting bolt to operate the spool. With this configuration, a pressure oil supplied into the sleeve is delivered from a through-opening in the sleeve to the outer surface thereof, and the pressure oil is controlled by the spool so that the supply and discharge of the pressure oil to and from two pressure chambers are realized.
In addition, JP 2009-515090 A (Reference 2) discloses a technology in which a valve housing is accommodated in a connecting bolt (a central piston in Reference 2). In the technology of Reference 2, a sleeve (a pressure medium guiding insert) is provided as a valve housing inside the connecting bolt, a spool (a control piston) is movably accommodated inside the sleeve, and an electrical adjustment unit is provided outside the connecting bolt to operate the spool.
In addition, JP 2016-048043 A (Reference 3) discloses a technology in which a spool is provided in a connecting bolt, so that a hydraulic oil is controlled by moving the spool from the outside, and a sleeve is fitted onto the bolt. In the technology of Reference 3, an introduction path, which supplies the hydraulic oil from an oil pump to the sleeve, is formed between the outer periphery of the connecting bolt and the inner periphery of the sleeve.
A configuration in which a valve unit is provided inside the connecting bolt to control the hydraulic oil as described in References 1 to 3 may reduce a distance between an advanced angle chamber or a retarded angle chamber, which is formed between the driving side rotator and the driven side rotator, and the valve unit. Thus, the pressure loss of a flow path is reduced and an operation having good responsiveness is implemented.
In addition, as in the configuration of Reference 2, a valve unit, in which the sleeve is fitted into the inner space of the connecting bolt and the spool is slidably accommodated inside the sleeve, enables the number of oil paths to be reduced compared to the configuration of Reference 1.
Moreover, as a configuration for increasing responsiveness, when the spool (the hollow-shaped piston in Reference 1) is slidably fitted onto the sleeve as in the configuration of Reference 1, it is possible to directly supply the hydraulic oil to the spool from the inside of the spool. Thus, pressure loss hardly occurs and responsiveness can be improved.
However, in the configuration of Reference 1, since the spool slides along the inner surface of the connecting bolt and at the same time, the spool slides along the outer surface of the sleeve, it is necessary to make the axis of the inner surface of the connecting bolt, the axis of the spool, and the axis of the outer surface of the sleeve to be coincident with each other with a high accuracy, which makes manufacturing difficult.
In addition, it is considered that, when the accuracy required in this configuration cannot be maintained, the sliding resistance of the sleeve is increased and a smooth operation is difficult.
Considering from the viewpoint of responsiveness, a combination of effective configurations described in the respective documents is conceivable. However, for example, a configuration, in which the sleeve is fitted into the inner space of the connecting bolt, the spool is slidably accommodated inside the sleeve, and a cylindrical member is disposed inside the spool to supply a hydraulic oil, requires strict accuracy management, and thus, there is room for improvement.
Thus, a need exists for a valve opening/closing timing control apparatus which is not susceptible to the drawback mentioned above.